1. Field of the Invention
This invention relates generally to compositions which may be applied to the surface of highway pavements, sidewalks, patios and other concrete and bituminous concrete structures to protect such structures from destructive surface spalling which results when the pores of such structures are subjected to stresses created by the expansion and contraction of water or water based solutions during a freeze-thaw cycle. More specifically, this invention is directed to compositions, methods and surface applications of carboxy methyl cellulose to concrete surfaces during ice and snow removal operations in order to decrease the amount of surface deterioration which occurs as the liquids which are covering or absorbed into such surfaces are subjected to cycles of freezing and above freezing temperatures.
2. History of the Prior Art
One of the greatest problems of maintaining concrete, primarily when in the form of walkways, roads, and highways, is the rate at which the concrete breaks up. The cost of repairs and replacement of such concrete amounts to millions of dollars each year.
Much research has been done in an attempt to protect concrete surfaces which are subjected to being flooded or covered by water from the spalling effect which results from repeated freeze-thaw cycles of the water in response to climatic conditions. Most of this work has been done in the field of developing protective coatings and through the use of air-entrained concrete. However, little effort has been directed to developing compounds which could be applied to a concrete surface in the presence of ice, snow, water or water based solutions containing de-icing salts, urea and the like.
The surface spalling of concrete is a result of the stresses created in water, which has soaked into the surface pores of the concrete, is expanded as the ambient temperature drops below freezing. If during the repeated cycle of freezing and thawing of the water within the pores of the concrete, these stresses should exceed the yield point, the surface will become cracked and chipped.
Further, it is well known in the concrete industry that the use of many de-icing compounds, such as a common road salt, may actually increase the rate of surface spalling dependent upon the particular type of concrete involved and the resultant concentration of salt solution involved. When de-icing salts and de-icing solutions are used to melt snow or ice on a concrete surface, the ice or snow is changed to a liquid state and forms brine solutions which may vary from about zero percent brine to a saturated brine solution. When the air temperature becomes sufficiently low, the solution which has been absorbed into the concrete expands upon being frozen and creates a stress in the concrete. Again, if the stress exceeds the yield point, the concrete fractures and spalling occurs.
Although research substantiates the fact that salt increases the rate of spalling of non-air-entrained concrete, it also shows that salt decreases the rate of spalling of air-entrained concrete. Example 5 of the preferred embodiment shows that a 2.5% salt solution caused the non-air-entrained concrete to spall about 1.9 times as fast as did distilled water. However, in Example 6, distilled water spalls air-entrained concrete about 4.4 times as fast as a 1% salt solution in 395 freeze-thaw cycles and about 3.9 times as fast as a 2.5% salt solution in 919 freeze-thaw cycles, Example 7. Therefore, when applied to an air-entrained concrete, salt shows some degree of protecting action toward the reduction of the spalling which is caused by the freezing and thawing solutions which are in contact with or absorbed into the concrete.
In view of the foregoing, it is often the case that during conventional snow and ice removal operations, conditions are created which may be deleterious to the concrete surface. The Operator, Snow Fighter's Handbook for the Utah State Department of Highways, gives the following description of a method for maintaining bare highways during snowfall: "Begin salt application when the ground is BARELY WHITE and it is wet enough to hold the salt on the roadbed. It is really important that the salt is applied at this time because you are doing more than just applying salt--you are forming a brine cushion to `float` the snow layer on. This brine has two purposes: 1--It melts snow from the pavement up so that snow and ice don't stick to it, and 2--It `greases` the snow layer so that the snow plows can push it off the road more completely than without it." However, the presence of the brine solution within the pores of the concrete surface as the temperature falls creates a condition which may lead to surface spalling of non-air-entrained concrete.
Similar conditions are established by recommended de-icing operations for sidewalks. In the February 1973 issue of "Consumer Reports" is found the following directions for keeping the snow off of a sidewalk: "The temperature is within a couple of degrees of freezing, wet snow is falling and the forecast is for a total accumulation of two inches: Spread rock salt or calcium chloride at about one cup per square yard to melt the snow as it falls, or shovel."
The Portland Cement Association published in 1968 the "Concrete Information" pamphlet titled "Effect of Various Substances on Concrete and Protective Treatments, Where Required." This pamphlet is a recognized source of information on the known effects that many chemicals have on concrete. With the exception of protective coatings, no mention is made in the pamphlet of any chemical which would protect concrete against the deleterious effects which either freezing and thawing or any chemical may have on concrete. The following, however, is said of sodium and calcium chloride: "Frequently used as a de-icer for concrete pavements. If the concrete contains insufficient entrained air or has not been air dried for at least 30 days after completion of curing, repeated application may cause surface scaling." Further under the heading of Miscellaneous, the following statement is made: "Chlorides (calcium and sodium), urea and ethyl alcohol cause scaling of non-air-entrained concrete."
In order to combat the damaging effects to concrete from de-icers, the pamphlet lists the following protective coatings: "50% solution of boiled linseed oil in kerosene, soybean oil, modified castor oil, sand filled epoxy or coal-tar epoxy."
In addition to the aforementioned conditions, many factors affect the rate at which concrete, under freeze-thaw conditions, may break up. Some of these factors are the relative amounts of aggregate, water and cement in a batch of concrete, the amount of mixing given to a batch of concrete, the amount of agitation given to the concrete after it is in place and before it has set, the chemical composition of the cement, the fineness of the cement, the conditions under which the concrete is cured; the conditions under which the concrete is allowed to dry, the amount of water that is held in contact with concrete during the freeze-thaw cycle, the lowest temperature attained in the freeze-thaw cycle, and the number of freeze-thaw cycles to which the concrete is subjected.
As the use of chemical de-icing compounds is widespread in snow or ice removal operations, it would be extremely beneficial to provide some additive or other means by which the concrete pavements and other such surfaces could be protected from the spalling due to the presence of water or various solutions which result from melting ice and snow.
Further, due to the time, available equipment, and expense involved, it would be advantageous to apply a spalling protective agent simultaneously with conventional road salting or spreading operations.
Some examples of the prior art include:
U.S. Pat. Nos. 2,154,220 to Sponsel, 2,192,320 to McCarthy, 2,570,827 to Madison et al, 2,731,353 to Fain et al, 2,948,625 to MacKenzie, and 3,556,718 to Bachmann et al, and publications Chemical Abstracts, Vol. 71:84296c, 1969 and Chemical Abstracts, Vol. 73:123244x, 1970.